Cameras are incorporated into many kinds of mobile devices such as cell phones, smart phones tablets and the like so much that nowadays virtually every mobile device includes a camera. Initially the camera's function was simply to take pictures, but many cameras are now also used for additional functions such as user identification and validation, gesture recognition, and so on. For various reasons many of these additional functions must be carried out using non-visible (i.e., invisible) light such as infrared, and so the mobile devices must also include some kind of radiation (i.e., light) source that provides the needed non-visible radiation.
Many mobile devices operate using batteries and are therefore power-constrained—that is, they can provide only a limited amount of power before the battery runs out and must be recharged. Regardless of battery capacity, too-short battery life (how long a battery lasts between charges) is a constant user complaint. But in most devices that have a non-visible light source it is used is very inefficiently, meaning that the non-visible light source drains more power than needed from the battery and leads to a shorter battery life than necessary.